A patient with electrocardiogram changes in leads V3 and V4 that reflect an infarction is experiencing an injury to which area of the heart?

• A. Inferior
• B. Anterior
• C. Lateral
• D. Posterior

Answer: (B)

The chest leads over the heart map to specific regions of the left ventricle, and V3 and V4 sit on the anterior surface. When infarction occurs, changes in these anterior-facing leads localize the injury to the anterior wall of the left ventricle. This area is supplied primarily by the left anterior descending artery, so ST changes in V3 and V4 point to an anterior-wall myocardial infarction. Other regions have distinct patterns (for example, inferior changes show up in II, III, and aVF, while lateral changes appear in I, aVL, V5–V6), and posterior injuries often show reciprocal changes in V1–V3.